Functional capabilities of synaptic terminals can be studied with morphologic methods. Terminals are subject to structural alteration in response to normally occurring biological events such as development. The activities can be followed with biochemical markers which can subsequently be visualized autoradiographically and histochemically. The objectives of this study are: 1) to analyze the basic structure of auditory terminals and their natural changes; and 2) to correlate the structure with biochemical characteristics of terminals demonstrated morphologically. Such information will enhance our understanding of the morphological bases for physiological events and information processing capabilities of these nuclei. Terminals in the medial superior olivary nucleus (MSO) have been chosen for study because the structural and synaptic organization of this nucleus are well understood and especially advantageous for the experiments planned. Terminals in other brain stem auditory nuclei will also be considered because of the features (including the presences of an intercellular substance) common to some classes of auditory terminals and the distribution of collaterals of auditory axons to these nuclei. Normal kittens, cats and inbred mice (C57B1/6) will be used. Electron microscopic analysis of Golgi material will be used to correlate classes of axon terminal arbors with ultrastructurally defined synaptic terminal classes in the MSO. Horseradish peroxidase and I125 alpha-bungarotoxin will be used to localize acetylcholine receptor sites in auditory nuclei. Uptake of H3-GABA and H3-glycine by auditory neurons and terminals will be studied in brain stem slices. EM autoradiography will be used to study relationships between terminals and their internal and surrounding structures.